1. Field of the Invention
The present invention relates to a process for producing a molded printed material, and to a molded printed material.
2. Description of the Related Art
Molded printed materials such as molded printed sheets (decorative sheets) are used today in various applications. For example, the surface sheet of a membrane switch used in an electrical product, etc. is produced by forming an image on a thin plastic sheet (PET, polycarbonate, polystyrene, etc. having a film thickness of about 100 μm) and then embossing it in order to impart a click feel to a switch portion (click portion). Furthermore, there are many cases in which, in order to give a printed material a matte appearance or a three-dimensional feel in design, the printed material is subjected to embossing.
Moreover, drink product vending machines for drinking water, tea, juice, etc. are widespread, and these vending machines display dummy display items of products for sale. As such dummy display items, a flat support that is formed by subjecting a transparent thermoplastic resin sheet to decorative printing is deep drawn to give a halved shape of an actual-size drink product container, thus forming a deep-drawn molding with a rise of 25 mm or higher in some cases, and the back face is illuminated so as to give a strong appeal to the product image.
As a process for producing a deep-draw molding from such a decorative thermoplastic resin sheet, vacuum forming, pressure forming, or vacuum/pressure forming is most suitable. In principle, vacuum forming involves preheating a flat support to a temperature at which it can be thermally deformed, and pressing and cooling it against a mold while drawing it to the mold by means of reduced pressure, and pressure forming involves pressing and cooling it against a mold while applying pressure from the side opposite to the mold. Vacuum/pressure forming involves carrying out the reduction in pressure and the application of pressure at the same time.
Therefore, in embossing, vacuum forming, pressure forming, and vacuum/pressure forming (hereinafter, called ‘vacuum forming, etc.’), since a thermoplastic resin sheet used as a substrate is required to have a high degree of stretchability in a heated state, a polycarbonate resin sheet, a polyester resin sheet, a cured vinyl chloride resin sheet, a polystyrene resin sheet, etc. are generally used, and from the viewpoint of ease of decorative printing and various resistance properties of a molding formed by vacuum forming, etc. being excellent, a polycarbonate resin sheet or a polyester resin sheet, and in particular a polycarbonate resin sheet, is most suitably used. As the thermoplastic resin sheet, one having a thickness of on the order of 0.1 to 0.8 mm, and preferably on the order of 0.3 to 0.6 mm, is generally used.
Furthermore, for decorating the above sheet a solvent-based ink composition containing a colorant such as a pigment as an ink and, as a binder, a vinyl chloride copolymer, a solvent-soluble polyester resin, an acrylic resin, etc. is normally used. A decorative printed layer that has been printed using such an ink is very suitably used since it exhibits good stretchability in vacuum forming, etc. by conforming to the substrate sheet in a heated state.
However, in the above-mentioned conventional method, since a solvent-based ink composition is used, there is the environmental problem that the solvent must be removed by evaporation, and there is the difficulty that thermal energy and drying time for removing the solvent by evaporation are required.
From such a viewpoint, printing a thermoplastic resin sheet using a UV-curing ink composition, which does not employ a solvent, and then processing it has been proposed (Japanese Patent No. 3119282). However, this proposal relates to cold bending, or to pressing or thermal pressing in which the rise angle is as small as on the order of 45° and the draw depth is as small as on the order of only 5 mm, and no attempt has been made to use a UV-curing colored ink composition for decorating a deep-drawn vacuum-formed product in which the sheet is drawn by a factor of several times.
Conventionally, as a printing method for obtaining a printed sheet (decorative sheet) to which molding is applied, a printing method employing a printing plate such as offset printing, screen printing, or gravure printing is used. These printing methods require an expensive printing system and preparation of a printing plate, and are not suitable for small-scale production because of the cost and effort.
On the other hand, in the inkjet method, the printing system is inexpensive, and no plate is required for printing; since an image is formed directly on a recording medium by discharging ink composition only onto a required image area, the ink composition can be used efficiently, and the running cost is low, particularly in small lot production. Moreover, the inkjet method has attracted attention in recent years since noise is low and it is excellent as an image recording method.
In particular, with regard to an inkjet recording ink composition that can be cured by irradiation with radiation such as ultraviolet rays (radiation curing type inkjet recording ink composition), since a majority of the component of the ink composition is cured by irradiation with radiation such as ultraviolet rays, the drying properties are excellent compared with a solvent-based ink composition and, furthermore, since an image obtained is resistant to spreading, the method can be applied to the printing of various types of substrate.
There is a demand for a radiation curing type ink composition that cures with high sensitivity in order to form a high quality image.
By achieving higher sensitivity for the ink composition, high curability upon exposure to actinic radiation can be imparted, and there are therefore provided various benefits such as a reduction in power consumption, longer lifetime of an actinic radiation generator due to a decrease in the load thereon, and suppression of evaporation of uncured low molecular weight material and of a reduction in the strength of an image formed.
Furthermore, there is a desire for an ink composition that gives an image (printed material) that is resistant to cracking, peeling off, etc., and gives a cured film that has excellent impact resistance, flexibility, and adhesion to a substrate. A cured film having high flexibility, impact resistance, and adhesion to a substrate enables a printed material to be displayed or stored for a long period of time in various environments while maintaining high image quality, and also has advantages such as ease of handling of the printed material.
An ink composition used for obtaining a molded printed sheet (decorative sheet) is required to have a high level of cured film flexibility since an ink coating is stretched during molding. Furthermore, it is necessary for the cured film to have a strength that can withstand molding. Conventionally, ink compositions having high flexibility have been disclosed (International Patent Applications WO 2002/038688 and WO 2005/026270), but they have the problems that the film strength is insufficient, scratches or pinholes are caused on an image during molding, and cracks occur due to poor resistance to stretching.
Moreover, an ink composition that can be used in vacuum forming or pressure forming and can be cured by irradiation with radiation such as ultraviolet rays has been disclosed (JP-A-2003-326591 (JP-A denotes a Japanese unexamined patent application publication)), but it has high viscosity and cannot be applied to the inkjet method.